It has been reported that volatiles from broad bean plants, Vicia faba (cv. ‘the Sutton’) infested by the pea aphid, Acyrthosiphon pisum, attract a specialist parasitoid Aphidius ervi, collected from populations in England, Italy and Bulgaria, which had no previous experience of the host-infested plant volatiles. Aphidius ervi collected in Hokkaido, Japan were also attracted to volatiles from host-infested broad bean plants (cv. ‘Nintoku Issun’) in preference to those from intact plants in a Y-tube olfactometer when the wasps were allowed to emerge on the infested plants, but wasps that had emerged in a clean Petri dish showed no significant choice between the two odor sources. When artificially exposed to the infested plant volatiles during emergence from the mummy, the wasps showed a significant preference for infested plant volatiles over those from intact plants. In further studies in a wind tunnel, significantly more wasps landed on infested plants than on intact plants when wasps were exposed to infested plant volatiles. Naïve wasps, however, did not show a higher landing response to infested plants. These data suggest that learning is required by A. ervi of the Hokkaido strain for their response to infested plant volatiles in their host searching behavior.